There is no set rate for school properties. To my knowledge there is no such property listed for lease in the Sunland/Sylmar area. Such a property would be listed under Commercial or "Special Purpose" on Commercial Listing web sites. To calculate a suitable lease rate is a fairly complex process and involves a number of factors such as total square footage of improvements (usable and rentable), lot size, Income potential, length of lease, highest and best use of the property, uniqueness of the property, demand for such properties, property owner's expenses, etc.
You have not specified what kind of school you are looking for. You may also be aware that the City/State/Federal laws may dictate certain space requirements for schools and you also may need to obtain licenses and other approvals from the authorities before entering into a binding lease agreement. An Attorney's and Accountant's advice would also be strongly recommended in this case.
Certified Commercial Investment Member (CCIM)
United America Realty