Can My Brother Grow By Just Staying Horizontal?

A page about it in the online version

Can My Brother Grow By Just Staying Horizontal? was a science project by Greg in Diary of a Wimpy Kid (online) and Diary of a Wimpy Kid: Rodrick Rules. Greg sees Rodrick lying on the couch for a long time and wonders if he will still grow despite being in a horizontal position. Greg does not turn in his project after tracking that Rodrick grew normally in a month.