I gave it a good once-over with primer before painting two coats of green. The green paint was turned into chalkboard paint by adding a heaping spoonful of grout. The chipboard surface is still pretty rough even after painting so it might not actually work out as a chalkboard. It was worth a shot. I also added grout to a small sample tub of gray paint for the road.
Ryan cut scrap boards into little block houses and each kiddo painted one. The girls also painted two blocks as a school and a store.
The blue paint was leftover homemade chalkboard paint from another project. The only thing I actually purchased for this project was a pack of chalk markers I used to draw the details on the road.