I live in Frisco and my son, who just turned 5 has been going to Preston Ridge Preporitory Preschool (on Hillcrest in between Lebannon and College) since he was about your son's age. Like you, I worked part-time and would put him in school from around 8:30 am to around 3 pm. The regional director (Laura), school director (Ashley), and assistant director (Rachel) have all been apart of this school since it was opened back in 1996. The teacher turn over rate is low too. Which is very important to me since my kiddo gets attached. They have a great cirriculum even for your son's age and they do take time out for naps. Give them a call....###-###-####