'1. He's six. He doesn't know what he wants or needs.'
I beg to differ-one of my three children had very clear ideas of what she wanted by six.
Children of this age can be involved in choices in their lives-we see it very often in the autonomous home educating community.
'2. Doing this [if it were allowed and it shouldn't be] will lead him to believe that you can just pick and choose the best/most fun bits out of any activity and life just isn't like that.'
It is allowed if the headteacher agrees.
Flexischooled children do just that-pick the bits of a school curriculum which suits that that child.
This is personalised education we are talking about-and certainly our children's lives were like that, they picked the best/most fun bits all of the time.
The older two are in the world of work now, in jobs of their own choosing, that they enjoy. They continue to coose to do activities that they find fun and don't do things they don't want to do.
I do the same.
'3. It would be most unfair on other children to see him swan in and out as the mood takes him [or you].'
IME flexischooling is negotaiated by the parent and headteacher, where the the classes the child will attends is agreed, rather than the 'swanning in and out'. However I do know of one friend whose child goes to school for the majority of the time, but has days out whenever something more interesting/educational comes up-this again was negotiated by the parent and the head when the child started that school.
This has nothing to do with fairness to others. All parents have the same responsibility under Section 7 of the 1996 Education Act:
The parent of every child of compulsory school age shall cause him to receive efficient full time education suitable
a) to his age ability and aptitude,
and b) any special educational needs he may have, either by attendance at a school or otherwise.
The majority of parents choose to delegate this responsibility to the state and send their children to state school.
Some parents use Public Schools, others Home Educate and some Flexischool.
Whilst flexischooling would not be the choice my children would make with me about their education, the OP may well choose it as the best way to deliver a suitable and efficient education for her child-to fulfill her responsibility.
Parents in the vast majority of cases want what is best for their child and should be given accurate info about all the educational choices available, so that they can make an informed decision on what is right for their family at that time.