By Matt Harrington, BCBA · Behaviorist Book Club · Research-backed answers for behavior analysts
The available evidence consistently indicates that teaching manual signs does not delay or prevent vocal speech development. In fact, research, including the work by Carbone, Sweeney-Kerwin, Attanasio, and Kasper (2010), suggests that sign language training can facilitate the emergence of vocal behavior. Teaching signs provides a functional communication system that reduces frustration, establishes communication routines, and creates opportunities for vocalizations to emerge alongside signs. Practitioners should address this common concern directly with caregivers, presenting the evidence base while being honest that outcomes vary across individuals. The key principle is that sign training adds communication capability without removing any existing skills.
There is no single optimal prompt delay duration that applies to all learners. The delay should be individualized based on the child's response patterns and adjusted based on ongoing data. Most implementations begin with a zero-second delay to establish reliable sign manding, then increase to 2-5 seconds to create opportunities for vocal responding. The delay should be long enough to allow vocal responses to occur but not so long that the child becomes frustrated or disengaged. If the child is not producing vocalizations during the delay, increasing the interval alone is unlikely to be sufficient. Other procedural modifications, such as providing echoic prompts or increasing the reinforcement differential, may be necessary.
Vocal approximations should be reinforced, especially in the early stages of intervention. The goal is to increase the frequency of vocal responding first, then shape the topography toward more recognizable productions over time. Practitioners should define vocal approximation criteria in advance, specifying what counts as a reinforceable vocalization for each target. Initially, any vocalization that occurs during the prompt delay interval and bears some resemblance to the target may be reinforced. As vocal responding increases in frequency, criteria can be gradually tightened to require closer approximations. This shaping process should be guided by data and adjusted based on the child's progress.
Children with no existing vocalizations can still benefit from manual sign mand training, as it establishes functional communication. However, the prompt delay procedure may be less immediately effective at evoking vocal responses in children who have not yet demonstrated any vocal behavior. For these children, additional procedures may be needed to establish vocal responding, such as stimulus-stimulus pairing procedures to condition vocalizations as reinforcers, or intensive vocal imitation training. The sign mand training provides a critical foundation by establishing communication routines and motivation to communicate, which can support later vocal development when vocal responding does begin to emerge.
Mand training is often considered the most effective starting point for evoking vocalizations because mands are the only verbal operant that directly benefits the speaker. When a child mands, they receive the specific reinforcer they are currently motivated to access. This strong motivational component means that the child is more likely to exert effort to communicate, including producing vocalizations that may require more physical effort than signs. Other verbal operants such as tacts or intraverbals involve generalized reinforcement, which may not provide sufficient motivation for a child to attempt vocal responses during the early stages of communication development. Starting with mand training maximizes the conditions under which vocal behavior is most likely to emerge.
Practitioners should collect data on several dependent variables simultaneously. These include the frequency or rate of sign-only mands, vocal-only mands, and combined sign-plus-vocal mands per session. Recording the topographical accuracy of vocalizations using a simple rating scale can also be valuable. Probe data should be collected across settings, communication partners, and items to assess generalization. Additionally, tracking the latency between the presentation of the establishing operation and the vocal response provides information about the strength of the vocal mand repertoire. These multi-dimensional data sets allow practitioners to identify trends, make procedural adjustments, and communicate progress to caregivers and team members.
There is no fixed timeline, but practitioners should establish decision rules before beginning the intervention. A reasonable guideline might be to continue for 4-6 weeks of consistent implementation with good procedural fidelity before evaluating whether to modify or supplement the approach. If some vocal responding has emerged during this period, continuing with adjustments to the procedure is warranted. If no vocal responding has emerged despite consistent implementation, the practitioner should consider supplementary procedures, consult with colleagues who have expertise in communication intervention, and potentially explore augmentative communication devices. The child's overall communication progress, not just vocal development, should be considered when making these decisions.
Caregivers play a critical role because they interact with the child across the majority of waking hours and natural communication contexts. When caregivers are trained to implement prompt delay during natural mand opportunities, the child receives many more opportunities to produce vocal responses throughout the day. Caregiver training should include clear instruction on how to create establishing operations, how to implement the prompt delay, how to differentially reinforce vocal responses, and how to respond appropriately to sign-only mands. Practitioners should provide modeling, practice opportunities, and feedback to ensure caregivers can implement the procedure accurately. Regular check-ins with caregivers also provide valuable information about vocalizations that may be occurring outside of therapy sessions.
The research literature does not identify a specific age range where this procedure is maximally effective, though most published studies have involved young children, typically between 2 and 8 years of age. From a developmental perspective, earlier intervention is generally preferable because neural plasticity is greater in younger children and the gap between the child's communication abilities and age expectations is smaller. However, the underlying behavioral principles are not age-dependent, and the procedure can be adapted for older individuals who have not yet developed vocal communication. The key factors in determining candidacy are the individual's current communication repertoire, motor imitation abilities, and the presence of establishing operations that can motivate communication, not chronological age alone.
Manual sign training and AAC devices are not mutually exclusive approaches but rather different tools that can be used individually or in combination based on the child's needs. Signs offer the advantage of always being available and being physically promptable. AAC devices may offer advantages in terms of intelligibility to unfamiliar communication partners and the ability to produce more complex messages. Some children benefit from having access to both modalities. The decision about which approach to use should be based on a comprehensive assessment of the individual child's strengths, needs, and the contexts in which they need to communicate, consistent with the ethical obligation under Code 2.14 to select the most effective and least restrictive intervention for each individual.
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All behavior-analytic intervention is individualized. The information on this page is for educational purposes and does not constitute clinical advice. Treatment decisions should be informed by the best available published research, individualized assessment, and obtained with the informed consent of the client or their legal guardian. Behavior analysts are responsible for practicing within the boundaries of their competence and adhering to the BACB Ethics Code for Behavior Analysts.