It’s complex. Of course teachers who are unwell can’t be in school teaching and it’s usually not appropriate to be telling parents anything g at all about the reason for absence.
At the same time, schools do seem to manage it differently and some more successfully than others. Large schools in particular have more scope for shifting people around and finding a better solution. Constantly changing staff without continuity is a problem - although it’s a difficult one for schools to avoid. And a valid question is whether teacher prepared lessons delivered by the TA are the same or as good as when delivered by the teacher. There IS a difference, otherwise schools would use one teacher to plan everything and save large sums by getting it delivered by TAs. In fact, this is looking like the direction of travel in cash strapped education. So it’s not unreasonable for parents to ask why their child is only getting 50% or less of their time with a qualified teacher. Not quite clear if it would be better to have a string of qualified teachers or more continuity from a known TA - probably the latter, but that’s not suggesting it’s a great outcome.
Some schools seem to do better. They are more proactive in finding a replacement teacher for medium to long term needs. Some have contacts with individuals they will draw on and some have some really great contacts. Others seem to have none and some seem to want to avoid spending any money and to muddle through. Some Heads support muddling through for longer than others do. If asked by parents, many schools are defensive and vague and actually give answers which fob off. And it’s basically because the situation clearly is inferior to having their regular teacher, but they don’t want to say that.
What’s especially difficult is the illness that means a teacher takes a day off every week, the two days and then is around for a week and then off again..and it goes on for 3 months until they finally go off in long term sick. And until they are off more long term arranging anything semi permanent with consistency is very difficult. It might be controversial to say, but I think that teachers absolutely have the right to be off when they are sick, but some are very reluctant to communicate about their situation (I guess not unusual or surprising when mental health is involved especially) or likely future position and this makes planning for schools very tricky.
I recall when one of my DC was in Yr1, the 2 class share teachers were pregnant and due to go before Christmas. They were good and experienced and my heart fell when a very green teacher who had struggled to get a permanent job arrived. She really wasn’t great but my DC made enormous progress that year with reading and writing and maths. Honestly, I think they were just ready to progress snd didn’t need the best input….but that wasn’t the case for all the kids. The next year, we were told we were getting the very best teacher in the school for Yr2 - always had Yr2 to do their SATS and hugely experienced etc. We were thrilled and then within 2 weeks the poor woman went off with serious cancer. We didn’t see her again until May when she came in to see the kids for 2 days. Then there was a string of supply and TAs and although progress was made, it really felt like a poor experience. This was a 1 Form entry school, with very little slack or scope to move staff around. It wasn’t anyone’s fault and the schoo did their best, but it was all a bit shit for the kids. We moved then for Juniors to a 3 Form entry school. They also has maternity leave and absence etc, but it was very different. They just seemed to be in things in advance and also they communicated with families ahead of the known events. They boosted confidence by this, rather than the previous school which only ever communicated after whichever absence had already started snd even with the maternity leaves, only made contact the week before they started to say what was happening.
I think bright children who are ready to learn and suck things up, probably aren’t harmed too much in the infant years if they’ve already learned to read. Weaker ones though probably are far more. And Secondary is a different ball game. When you hear about the class who’ve had 6 different teachers through their Physics GCSE, with only 1 being a scientist, your heart falls. And it’s sadly very common. Even the classes with the qualified and capable teachers find they lose them as they are shunted away to a more ‘needy’ exam class. It’s understandable why it happens but gutting when your non exam class child loses their teacher again.
The thing is, this is all part and parcel of the funding and recruitment crisis in schools. There aren’t enough staff and when someone is off sick there’s aren’t enough to go round. Sadly, there will be more of this and disrupted educations and reducing expectations that even having a teacher all the time should be the norm.