This is damn good, impressive even. I normally look for things I don't like in pictures that I do like (hence the name Picky), but this is just so well done. It's actually the first of this gallery I've seen (a friend likes Cheerilee and linked it).
I guess for starters, Cheerilee's cutie mark looks a bit big. I didn't notice until the frowns on the flowers drew my attention (which are amusing, btw). Whoa, and Sweetie Belle's horn looks a bit big, too. Length seems to depend on height (Celestia's is very long and she's tall), and Sweetie Belle's looks a bit wide for her head and longer than Twilight's.
The hay-looking floor is good, but the wall seems so barren. Assuming they're in a young school (and this picture follows the floor in the episodes), it's so pale with only two pictures. It only gives us Cheerilee and Sweetie Belle to look at, whose colors contrast the pale wall in this elementary school? The idea is funny, the picture is neat, and the style is awesome, but more can always be done. This is far from cluttered.
Very good, and very cute. Love your style, but the cutie mark on Cheerilee is a bit big, but overall such great artwork.
I love the extra little details you did, like lines on the floor to make it look like hay, and paintings in the background. The shading was very well done, sometimes I see crappy shading.
One little thing though, I personally think Ms.Cheerilee's left eye's iris and pupil should go a little bit more to the right, she seems like she is looking past Sweetie Belle, to whatever student might be next to Sweetie Belle. Oh and one more thing, Sweetie Belle's horn seems a bit big.