My DS attended a DSP in years 4-6. There were 6 children, all year 3+. They said they did technically take younger children, but that the needs usually didn’t escalate until the children were a bit older so young ones were unusual. Supervision was 2:1.
DS has gone on to mainstream secondary, with 1:1 TA support. In a mainstream classroom, the focused support is essential, but in the DSP setting he was absolutely fine with 2:1 - there were fewer issues because fewer students.
We really liked the DSP set-up because DS was able to interact with mainstream students with a high level of interventions in the background. On days where his stress levels were high, he could spend the entire day in the DSP. Other days he spent almost entirely in the mainstream classroom.
We went back to mainstream thanks to the DSP. He probably would not have been able to handle mainstream secondary if we had stuck with mainstream primary. If we had gone specialist, he probably would have stuck with specialist because they didn’t seem to gear back to reintegration and that didn’t work for DS - he is academic and the specialist provision around here is not aimed at kids who want to go to university and DS wants to do space engineering.
It is worth finding out if the DSPs around you have kids who are roughly the same age - it won’t be great if your young DC is in with a bunch of year 5/6s. We have four primary DSPs in our borough and we were not given a choice, but it did work out well.
Also important to consider where you want it to go… is reintegration to mainstream your goal? Is specialist secondary the way to go? Around here there are DSPs in secondary schools as well, would that be an option when you get there?