Outcome for Children Receiving the Early Start Denver Model Before and After 48 Months.

The team looked at kids who got the Early Start Denver Model. They split the group at 48 months—kids who started younger and kids who started older.

Everyone got the same play-based ESDM sessions. The study simply compared how each age group looked before and after treatment.

Children who began ESDM before 48 months made much bigger jumps in verbal IQ. Both age groups improved daily-living skills, but autism severity scores stayed flat.

In short, earlier starts helped language most; other gains were smaller and equal across ages.

Giallo et al. (2014) saw the same early-start edge with classic EIBI: kids who began before age 2 gained the most joint attention and language.

Guthrie et al. (2023) ran an RCT and proved it experimentally—18-month starts beat 27-month starts on language and social skills.

Laister et al. (2021) add a twist: richer gesture use at intake predicts bigger ESDM language gains. So both age AND child skill at day one matter.

Eikeseth et al. (2007) calm late-start fears: beginning intensive ABA as late as 5–7 still tops eclectic care, showing kids aren’t “too old” for help.

If a toddler is waiting for ESDM, fight for the earliest slot you can get—every extra month may cost verbal IQ points. Still, don’t turn older preschoolers away; adaptive skills can grow even when language leaps are smaller. Use quick gesture screens at intake to spot who may need extra language support, and keep parent coaching strong for any start age.