By Matt Harrington, BCBA · Behaviorist Book Club · April 2026 · 12 min read

Developmental vs. Function-Based Assessment: Knowing When to Transition from VB-MAPP to EFL Programming

Overview & Clinical Significance

Two broad assessment and curriculum frameworks dominate clinical ABA programming for individuals with autism and developmental disabilities: developmental assessments, which organize skill targets along normative developmental trajectories, and function-based assessments, which organize skill targets according to the behavioral function they serve in the individual's natural environment. Understanding the conceptual foundations, clinical applications, and appropriate transitions between these frameworks is a core competency for BCBAs designing individualized ABA programs.

The VB-MAPP (Verbal Behavior Milestones Assessment and Placement Program) and the ABLLS-R are the most widely used developmental assessments in clinical ABA. They map verbal operant development and associated skills against developmental milestones, providing a structured sequence for programming with learners in early to middle language development stages. The Essential for Living (EFL) is the most prominent function-based alternative, organizing curriculum around skills that are essential for an individual's safety, independence, and quality of life in their natural environment, without reference to developmental sequence.

The clinical decision of when to transition from a developmental to a function-based curriculum is consequential. Remaining on developmental programming beyond the point of functional utility consumes instructional time on skills whose developmental sequencing matters less than their functional relevance to the individual's actual life. Transitioning too early may skip foundational skills that are prerequisites for more complex functional repertoires.

The BACB Ethics Code (2022) Section 2.01 on acting in the client's best interest requires that assessment and curriculum frameworks be selected based on what best serves each individual client's functional needs, not on clinician familiarity or program defaults. BCBAs who have never systematically evaluated whether their current framework matches their client's clinical profile may not be meeting this standard.

Background & Context

Developmental assessment in ABA has its roots in Skinner's Verbal Behavior framework and the subsequent work of researchers like Mark Sundberg, James Partington, and others who operationalized verbal behavior development into assessment tools. The VB-MAPP, published in 2008, provides a comprehensive assessment of verbal behavior milestones through a developmental lens, with barriers assessment for factors that impede language development and a placement and IEP goals component. Its wide adoption reflects both its clinical utility and the field's historical focus on language development as a primary programming target.

Function-based assessment approaches emerged from a different tradition — the foundational behavior-analytic emphasis on behavioral function and practical utility, combined with the growing recognition that many adolescent and adult learners with autism and IDD needed programming focused on life skills, safety, and independence rather than continued developmental language programming. Patrick McGreevy's Essential for Living, published in 2012, crystallized this alternative into a formal assessment and curriculum tool organized explicitly around functional skill categories: functional communication, self-care, safety skills, and community participation.

The distinction between developmental and function-based approaches is not simply a disagreement about which skills to target. It reflects a deeper difference in how learning objectives are conceptualized: developmental approaches ask where the learner falls on a normative developmental trajectory and what the next developmental step is, while function-based approaches ask what skills the learner needs right now to navigate their actual environment more safely and independently.

For many learners in early stages of language development, developmental programming is clearly appropriate — the developmental sequence provides a principled and empirically grounded ordering of instructional targets. For older learners or those who have progressed through early developmental programming without achieving the language fluency expected at higher developmental levels, continuing on a developmental trajectory may not serve their most pressing functional needs. This is the transition point that clinical judgment must navigate.

The organizational behavior management tradition is also relevant here: staff who have been trained to implement a specific curriculum approach may have significant investment in that approach, and curriculum transitions require careful management of staff behavior alongside the clinical case for the change.

Clinical Implications

The primary clinical indicator for considering a curriculum transition is a mismatch between the learner's developmental programming targets and their most pressing functional needs. A 16-year-old who has been working on VB-MAPP Milestones Level 2 targets for several years without significant progress may have skills that are developmentally assessed as lower-level but that are sufficient for meaningful functional programming on priority life skills. Continuing to target developmental milestones that are not progressing, while safety skills, independence, and community participation remain undeveloped, is a clinical priority problem.

EFL assessment systematically identifies the skills most critical for the learner's safety and independence, organized into priority categories. Skills that are rated as 'critical' in the EFL framework — emergency communication, basic self-care, safety skills — represent the highest-priority targets regardless of where they fall on a developmental sequence. A learner who cannot communicate an emergency or manage basic daily living activities but who is progressing on Level 2 VB-MAPP targets has an inverted clinical priority structure.

Curriculum frameworks should also be evaluated against the learner's age and daily context. A 6-year-old working on early developmental targets is in an appropriate context — developmental programming is designed for early language learners of any age. A 25-year-old working on the same targets in a group home is in a context where functional skills for daily life, employment, and community participation are more salient than developmental milestone attainment. The same curriculum target can be appropriate for one individual and inappropriate for another based on age, context, and life demands.

Hybrid approaches are common and often clinically appropriate. Many learners benefit from continued developmental programming for specific skill domains where they are making progress and where the developmental sequence is genuinely relevant, combined with function-based programming for the priority life skills that the developmental framework does not adequately address. The question is not always either/or but rather how to allocate instructional time to produce the best functional outcomes.

Transitioning from a primarily developmental to a primarily function-based curriculum requires intensive collaboration with families, who may have significant investment in the developmental milestones framework and may experience a transition as a lowering of expectations. Preparing families for this conversation — presenting the functional case for the transition, clarifying that functional skills build genuine quality of life, and addressing concerns about giving up on developmental progress — is a clinical competency that BCBAs need to develop.

Ethical Considerations

The BACB Ethics Code (2022) Section 3.01 on evidence-based practice is directly relevant to curriculum selection. BCBAs have an obligation to select assessment and curriculum frameworks based on the available evidence for their effectiveness with the specific population being served, not solely on familiarity or availability. The evidence bases for both VB-MAPP-based programming and function-based approaches are meaningful but not equivalent across all client profiles — the clinical literature supports different approaches for different learner profiles and clinical contexts.

Section 2.01 on acting in the client's best interest requires that instructional time be allocated to the skills most likely to improve the client's quality of life, safety, and independence. When a learner's most pressing functional needs are not being addressed because instructional time is consumed by developmental programming that is not producing generalized functional benefit, the allocation of instructional resources may not be meeting this standard.

Section 4.03 on supervision of behavior technicians is relevant to curriculum transitions. RBTs who have been trained extensively on a specific curriculum approach will need retraining and competency verification when a curriculum transition occurs. BCBAs are responsible for ensuring that supervisees are competent to implement whatever curriculum approach is used, and curriculum transitions must include the staff training component necessary to produce adequate implementation fidelity.

The communication of curriculum transitions to families implicates informed consent and transparency obligations. Families have a right to understand the rationale for clinical recommendations, including why the team is recommending a transition from one framework to another. Presenting the evidence, the clinical reasoning, and the anticipated benefits honestly — including acknowledging any uncertainty — is part of the ethical transparency that clinical practice requires.

Assessment & Decision-Making

A structured approach to the curriculum transition decision begins with a comparative analysis of current VB-MAPP or developmental assessment data alongside an EFL administration or needs analysis. Key questions include: What developmental skills are currently being targeted, and what is the progress rate and trajectory for those targets? What functional skill deficits does the EFL or similar needs analysis identify? Are the most critical functional needs — safety, emergency communication, basic self-care — being addressed in the current program?

Age-relative considerations should be explicit in the analysis. The same skill profile that warrants continued developmental programming at age 8 may warrant a functional reprioritization at age 14. This does not mean abandoning developmental programming but examining whether the balance of developmental versus functional targets reflects the learner's actual life needs at their current age and context.

Family priorities are a critical input. Some families have strong preferences for developmental milestone programming, either because they believe the developmental sequence is the right pathway to meaningful language development or because they are working toward specific educational or transition goals that require demonstrated progress on developmental measures. These preferences must be incorporated into the planning process, and the clinical case for any transition must be made in language that addresses the family's specific concerns and priorities.

Staff considerations include the training and experience of current staff with the proposed curriculum approach, the documentation and data systems that support each framework, and the organizational change management requirements of a curriculum transition. Curriculum transitions that are poorly managed produce implementation inconsistency that undermines clinical outcomes regardless of the quality of the clinical rationale.

What This Means for Your Practice

Review your current caseload and identify clients for whom the match between current curriculum framework and functional needs is worth explicit examination. For each learner on a developmental curriculum, ask: Is this learner making progress? Are the skills being targeted functionally relevant to their daily life? Are there critical functional needs — safety, communication, daily living — that are not being addressed in the current program?

Develop familiarity with the EFL or similar function-based assessment tools if you have not already. A clinical session spent administering or reviewing an EFL alongside a developmental assessment for a complex case will often clarify the curriculum transition question more rapidly than extended team discussion without that data foundation.

For the family conversation about curriculum transition, prepare specific, concrete examples of functional skills that would be targeted under a function-based approach and how those skills would improve the client's daily life. Families who can envision the practical benefits — a child who can ask for help in an emergency, who can manage basic hygiene independently, who can navigate a community setting — are more likely to engage constructively with the transition rationale than those who hear abstract curriculum framework arguments.

Apply OBM principles to the staff training dimension of curriculum transitions. Clear performance expectations, training with competency verification, initial high-frequency feedback, and systematic data on implementation fidelity are the essential ingredients for successful curriculum transitions in clinical ABA settings. Staff who understand the clinical rationale for the change and who receive adequate preparation are more likely to implement new procedures with fidelity and to maintain that fidelity over time.