I give them 3 different payment options.
1) pay a higher rate between Sept and April (college/university)
2) pay higher rate between Sept and June (elem. or high school)
3) pay my regular rate year round.

they end up paying me the same amount no matter which option the choose. I put X amount aside from option 1 & 2 payments to cover over the summer. they still pay for March break and christmas. I basically have a "summer holding fee" build into their tuition. The holding fee is non refundable and ONLY goes towards holding the spot. if they want care over the summer they have to either pay $10/day scheduled or pay option 3 and pay all year round.