Does abstract reasoning develop naturally, and does instruction/contri
bute to its development? In an attempt to answer these questions, this
article specifically focuses on effects of prolonged instruction on t
he development of abstract deductive reasoning and, more specifically,
on the development of understanding of logical necessity. It was hypo
thesized that instructional emphasis on the metalevel of deduction wit
hin a knowledge domain can amplify the development of deductive reason
ing both within and across this domain. The article presents 2 studies
that examine the development of understanding of logical necessity in
algebraic and verbal deductive reasoning. Ln the first study, algebra
ic and verbal reasoning tasks were administered to 450 younger and old
er adolescents selected across different instructional settings in Eng
land and in Russia. In the second study, algebraic and verbal reasonin
g tasks were administered to 287 Russian younger and older adolescents
selected across different instructional settings. The results support
the hypothesis, indicating that prolonged instruction with an emphasi
s on the metalevel of algebraic deduction contributes to the developme
nt of under standing of logical necessity in both algebraic and verbal
deductive reasoning. Findings also suggest that many adolescents do n
ot develop an understanding of logical necessity naturally.