Boys 'fiddling with themselves' in class

[Enihnus]

Sorry for the rather coy title, also I have name changed for this as may have to make a complaint etc.
I am a (female) trainee teacher in a secondary all boys school. I've seen more than one boy masturbating in class (Y 9, 10, 11). They do this while staring at me and smirking and it is intimidating. Ive no guidance on how to deal with this and I think my mentor has basically given up - it seems more or less accepted and behaviour is generally awful so I have no confidence in the department's ability to deal with it. Is this something you have experienced and how did you - and the school - deal with it? The utter rage and resentment I felt at having to prepare lessons for this group today makes me realize this may be the last straw for me in terms of the PGCE, but I'm interested to know how it should be dealt with.

I’m late to this and pleased to see you’ve reported it. It’s sexual harassment and your school should take it very seriously. If they dont, complain (formally) to your university or to the governors.

This is very strange. Boys in years 9, 10 and 11 are masturbating overtly in lessons you say? I find that very hard to believe. One boy possibly - even then I would be surprised - but boys in 3 different year groups, so at least 3 different classes?
As a trainee teacher, you should have a mentor who spends a lot of time in your classroom.
In 16 years of teaching - including my training - workng in challenging sec dary schools as an NQT, Head of Dept, Assistant Head Behaviour and Safeguarding and Deputy Head, I never dealt with one instance of this and I can think of few scenarios I have not dealt with in that time. I find what you are saying hard to believe.
I can not imagine how they are doing it? Hand in pants? Trousers unzipped exposng themselves? Seems very unlikely to me.

Lulu, I feel the same. So, SO unlikely.

I had a student masturbate whilst I was doing intervention with him as a TA. He did it quite often (though only once in front of me). He had ASD and genuinely didn't understand that it wasn't ok. To him, it felt nice, so why not?

This does not sound like a school at which a PGCE student should be placed. This behaviour is completely unacceptable. Your university should withdraw you from this placement.