I don't think that a photo this small will ever win here on DPChallenge. I just don't understand why any one would submit a photo without using ALL the resolution that is available to them. Good luck in this challenge.
Composition, perspective, dof all seem like very good choices to me. My only issues are a slight overexposure and a slanting chalkboard (they still use chalk?), but overall quite nice.
nice image - kind of small - but you can still make everything out. I like the green tone of coloring it has, the lighting on your main model seems a bit much - but I kind of like it as well as her expression :)
The greenish hue just isn't exciting me, but I do get the impression of this being her memory rather than her being physically present in a classroom of today.
Nice composition, expression, pose. Fix angle, and larger would be better, please see Learn > Tutorial > Using Photoshop to Prepare Photos for DPC Challenges