So September:
N1 (2 year olds) has 12 existing plus 12 new kids. They're now 3 and 2. Class could accommodate but need extra staff
N2 (3 year olds) has 30 existing, and 18 new kids. They're now 4 and 3. Need an extra room and staff.
Reception (4 year olds) has 30 existing and a handful of new starts who never went to nursery. They're mainly 5 with a handful of 4 year olds. Class can just about stretch of we abolish the 30 rule.
Year 1 (5 year olds) has 30 existing and 1 new. They're all 6 except the new one who never did reception. See above re 30 rule.
So our single form entry school needs at least 1 extra class room, and several years with intakes over 30. Some of the kids would have had no prior schooling, some will have had lots (good home schooling) and some a mixed bag. So school will have to accomodate all their learning needs.
Secondary schools are fine for 6-8 years and then will have the oversized years but probably have more space anyway. Primary schools can now sack their extra teachers.
However kids are now having to stop on until 19, and child benefit etc will need to be paid until then too. Presumably once the bulk year passes, it will revert to 18
In 12-14 years there will be a significantly greater number of students applying which l, go en it's unlikely universities will increase numbers but this will likely impact for much longer as students reapply for several years.
Simple.
OR we have faith in teachers to be able to teach students at their different levels, which they already do.
Exam years we accept that some students will choose to repeat the year but it won't be all students so the impact on higher education will be less significant