It's not a case of "sticking up for" the 7% who choose private education. I wish that type of education were available to every child in the country, but that would be impossible for any government to finance.
Like several others here, I believe Corbyn was wrong to bring the funding of school meals into the subject. It makes it such an emotive issue. It would have been better to have concentrated on something educational, like more resources, more facilities, more staff.
Interestingly, the cost of a lunch in a private prep school is around £5 per head, whereas the average state school lunch is £2 per meal. Thee will always be inequalities.