I am running a model with which I want to explain students' performances. I lagged my main independent variable by two years. Now, my results show a negative coefficient for the two years lagged independent variable. However, when I add a higher lag of that IV - let's say a three or 4 years lag - the coeeficient of the two years lagged IV becomes postive while the higher lags are negative.

Is that normal? How do I interprete these results?

Could it be that my highest lag (in this case lag2) also represents higher lags?

Sorry for any wordiness and thank you very much for your help.

I'm running a TSCS analysis with the plm library in R with which I want to explain students' performances. The data consist of approximately 1100 units and has 25 points of measurement - panel data with ~27,000 units. I lagged my main independent variable by two years. Now, my results show a negative coefficient for the two years lagged independent variable. However, when I add a higher lag of that IV - let's say a three or 4 years lag - the coefficient of the two years lagged IV becomes positive while the higher lags are negative.

Is that normal? How do I interpret these results?

Could it be that my highest lag (in this case lag2) also represents higher lags?

Sorry for any wordiness and thank you very much for your help.