[R] question about cumulating random effects in lmer

[zhongmiao wang]

Hello:
I am studying the effect of schools on student achievement growth over
time. School effect is random. The effects of schools in prior years
are assumed to be persistent till the current year. Thus, the total
school effect in the second year is like J=J2+J1. Does anyone know how
to model this kind of cumulating random effects in lmer? Thanks in
advance!

Best Regards
Zhongmiao Wang