Flexi-schooling, where the child attends school part-time and is home educated the rest, is a legal option in England but, unlike full-time home ed, parents do not have an automatic right. They must have agreement from the child's Headteacher.
Here's all the official information a Headteacher should need :
Section 444 of the Education Act (1996) states:
(3) The child shall not be taken to have failed to attend regularly at the school by reason of his absence from the school—
(a) with leave,
(9) In this section “leave”, in relation to a school, means leave granted by any person authorised to do so by the governing body or proprietor of the school.'

The Current EHE Guidelines (section 5.6 page 18) :

5.6 “Flexi-schooling” or “flexible school attendance” is an arrangement between the parent and the school where the child is registered at school and attends the school only part time; the rest of the time the child is home educated (on authorised absence from school). This can be a long-term arrangement or a short-term measure for a particular reason. “Flexi-schooling” is a legal option provided that the head teacher at the school concerned agrees to the arrangement. The child will be required to follow the National Curriculum whilst at school but not whilst he or she is being educated at home. Local authorities should make sure that head teachers are made familiar with flexi-schooling and how it may work in practice. Further information is available in the DCSF’s guidance Keeping Pupil Registers.21
There has been some confusion as to what code should be used – the DCSF’s stance is:
‘Off-site activities which take place during the school's normal day can be recorded as approved educational activity, code B, but only if the activities meet the legislative requirements [see section 6(4) of The Education (Pupil Registration) (England) Regulations 2006] and the school has received confirmation that the activity took place during the session in question.
If the child was not undertaking educational activity, he/she should be recorded as authorised absence, code C.’

Section 6(4) :
(4) An approved educational activity is either—
(a) an activity which takes place outside the school premises and which is—
(i) approved by a person authorised in that behalf by the proprietor of the school;
(ii) of an educational nature, including work experience under Section 560 of the Education Act 1996 and a sporting activity; and
(iii) supervised by a person authorised in that behalf by the proprietor or the head teacher of the school; or
(b) attendance at another school at which the pupil is a registered pupil
© Lancashire Home Education Forum Group Website generously hosted by Flump