Johnson and Astros broadcaster Bill Brown read "William is Going Green" to Shannon Warren's sixth to eighth grade special needs class, which earned the recognition after Warren won a contest with an essay detailing her class's recycling projects.
"Those kids love it when we get to come in and take pictures and sign autographs," Johnson said. "Seeing the smiles on those kids' faces makes my day, so it was awesome."
The class was also recognized before Tuesday's game against the Cubs at Minute Maid Park.
The book emphasizes the importance of recycling in keeping a healthy environment. It also details the importance of the little things, like donating old toys or turning off the lights when they aren't needed.
Johnson has been the Astros' Play Green ambassador for a couple years now and does two or three school visits a year.
"It's not one of those paid deals that you do," Johnson said. "This is strictly [volunteering] that I do. It's something cool to go out every once in a while and see the kids. It makes it worth it to see the smiles on their faces."