I do not know of any authoritative research.

However I can tell you my anecdotal experience from watching my children who are now using microsoft teams for their school classes.

The age and motivation of the child are relevant to the attention span.

My 5 year old will not sit still for their classes without adult supervision. However my 16 year old will sit through the lesson and seems to watch the screen. Whether she is actually paying attention or learning anything is another matter.

Your question recalls to me some data from the pedagogical classic. ''What's the Use of Lectures?' by Donald Bligh. Most of these findings would apply to any educational presentation, regardless of form.

I recall a graph, which was generated by hooking up audience members to respirometers and pulsometers during an extended lecture. Attention is greatest in the first 10-15 min, then sinks into 'Death Valley' until the last 5 min. Attention perks up when there are changes in presentation mode or interpersonal interactions. The more challenging/confronting the interactions, the more attention. Breaks reset the whole clock to some extent.

So it stands to reason that one must build in many small blocks of differently-styled content, force as many interactions as possible, and by all means schedule breaks.

The age and motivation of the child are relevant to the attention span.

Agreeing with the above mentioned fact

Thank you all.