I used the CMYK46 avatar and these dummies for reference.

Make the sketch

Fill a new layer with a light brown and pick a drak brown for the background color, go to menu Filter > Render > Fibers to create the wood texture.
Cut some parts of the new texture to make the chalkboard frame, merge these layer when finished
On a new layer behind the frame fill a layer with a dark green to complete the chalkboard.

Select the frame layer and go to menu, Layer > Layer Style.... apply drop shadow, belvel and emboss, and satin with a dark brown

Begin to draw the basic shapes, I changed a bit the positon of the figures here.

Warp the textures to make them fit to the bodies and begin to paint thee shadows

Improve the shadows ans add some details using some layers in multiply mode

Use another layer in overlay mode to make the highlights

Make a new layer and fill it with a light brown, on another layer in front of this one apply menu Filter > Noise > Add Noise... and set the blending mode for this layer to overlay, reduce the opacity of this layer to make only a subtle texture effect.
Do the same for the ground texture, in this case merge both layers and tranform them to make the perspective.
Add some brush strokes to the wall and to the floor to make them look a bit rough
Draw the hair with a brush made of a thin line and finished