It not bad per say it really depends on 3factors
personality of the child
school
the teachers themselves.
dd1 had job share teachers for reception as was 1st year 1st child dident realy overanalyse if this was good or bad thing.
one did 3days and was teaching longer bit shouty and strict but dd1 liked her better than newly qualified softer younger one who did 2days.
She had an ok reception year except the older one who was suppost to work 3days was frequently sick so lots of supply which not great I think with reception they could really d with 1 experinced teacher but woder as efys maybe its least worst place they can dump a rubbish teacher do least harm.
There was one mum at school who also taught at the school, peronally want to teach at same school as my chiild.
she covered a few of dd1 lessons.
But heared all sorts things that for her it was just a job that fitted in around her life she never put in the extra mile was a job of convieniance.
That she relucatantly took on 1 extra day when asked.
but dd1 then had 1 teacher in year 1 and had crap year 1 even though she adored the teacher she made little progress.
I think job shares are mre commn at some schools that others.
we moved schools after 1 term, then the new teacher at the new school ave notice so had 3teachers for year 2 in total.
4-5 if yu cunt diffrent one for pe, personal planning time and higher level ta teaching re.
she somehow had fab year and progressed.
Only 1 class in new school had job share year 4/5 but the strict one who did 3days has moved areas so left and left the younger nice newly qualified doing 5days and now parents are moaning that they liked the job share that childs not being pushed enough I will have reserve judgement dd1 in that class next year and 2years in that class but will have trust head will act accordingly and this year was bit of hiccup and make do year.
But freinds at old school had job share for their year 3 and its been disaster mainly because one one who did the mst days has been long term sick again shes been there 10years we were there 2years 1 term and never met the woman so they had loads of supply teachers.
when dd1 was at old school 1 class had teacher who was deputy head then head went sick and that year that class got messed abut as she was busy with headship duties and class had n continuity.
They need to have a plan, communicate and mesh well and think maybe reception, year 6 possibly year 2 benefit from just 1teacher.