I would expect that the CSO is doing the following...

~ Trying to establish how the child is doing in class and in the play ground.

~ Trying to establish what the child's education is like - how well or how badly they are doing.

~ Trying to gain information on how regularly the biological relatives are or were involved with the school.

~ Trying to possibly obtain access to the child's school file (some teachers keep the files in the classroom).

~ Trying to gain information on what the child's school lunches are like - if the child comes to school in or out of uniform - whether the uniform/clothing is clean or dirty.

~ Trying to find out whether the child attends school regularly - is often or always late - whether absences are mysterious or accompanied by a letter from the parent.

I would treat the knowledge of the CSO speaking privately with the teacher as a head's up... DoCS are very good at making something out of nothing.

It may be that it's common practice for the school to allow DoCS to speak with teachers alone... I would contact the principal and query them about that.

I've found that many schools actually have no idea where they legally stand in regard to DoCS and therefore follow the lead of DoCS even when they shouldn't.

I had an instance where the previous school my children were attending was absolutely ignorant. They wouldn't make a move until they got the green light from DoCS.

I ended up writing a very terse letter to the principal and informing him that I maintained guardianship of my children and if I gave the approval for X to occur then it was to occur and had nothing to do with permission from the carer or the CSO.