First of all, according to the relevant laws and regulations, the school land supporting public construction should belong to the public utility land allocated by the government. The above-ground buildings allocated land cannot be sold like commercial houses, and generally have the right to use for 50 years. That is to say, in most cases, these lands cannot be directly transferred or sold.
However, if the land occupied by the school is residential, the developer bought the whole land with residential land and planned to build a private primary school by himself. If the planning of the school is approved by the planning department, then the land use right and property right of the school should be owned by the developer, and the school or school land should be transferable at this time.
In a word, whether the land for supporting public schools can be transferred or sold after the housing is completed depends on the relevant laws and regulations and the actual situation. It is suggested that you should seek professional legal advice when considering such issues to ensure that your rights and interests are fully protected.