We examined the acquisition of incidental information and observational lea
rning of incidental information by adolescents with moderate intellectual d
isabilities during school-directed systematic instruction Effectiveness of
constant time-delay instruction for vocational-skill acquisition was evalua
ted within a multiple-probe design across sir dyads. Dyadic instructional a
rrangements allowed the assess ment of incidental information acquired thro
ugh observation. The constant time-delay procedure was effective in teachin
g the target vocational skill. In addition, participants acquired and retai
ned approximately 50% of the incidental information to which they were expo
sed during the consequent events of constant time-delay instruction either
through direct verbal presentation or through observation of their peers' i
nstruction. (C) 1999 Elsevier Science Ltd.