Nobody knows. Schools might be preparing for opening, but we also prepared for closing for a month before it was announced. We watched the same press conference about school closure as everyone else, no official early warnings.
Schools were given no central government support to arrange closure, first info from them direct to schools about it, arrived Sunday night after we closed. Some local authorities were more helpful than others. Everything that was organised, was organised by the schools themselves until 2 weeks in to lock down. Even now the DfE is still messing up free school meal vouchers.
If schools are prepping for return, then that's the reason. We'll get the same warning as everyone else, and we'll have to organise distancing or whatever, ourselves. No reason to think that any prep is about a specific date, or being done with prior knowledge.
There is no way to do primary school with social distancing without it not really being normal school. If it was normal, then that would be the end of any lock down options, and would probably cause a second peak - not because children get it or pass it, but because of how community works around a school. I've seen Holland saying no issues with schools, and Germany saying schools were a hub of the virus. So who knows.
My advice would be to expect September, be happily surprised by a summer term date. All teachers want to go back to school in a safe way. What we're being asked to do right now is awful and extremely stressful.