Predicted grades lower than mock results?

I teach English so this won’t be the same as all subjects.

Reasons for a lower predicted grade than mock grade (for me) include:

• If they have only sat one paper (e.g. paper 2 for language is much harder than paper 1)
• Class work/general work ethic (mocks are often less intense than the real exams - only half the papers, well spread out exams etc)
• Level of scaffolding/help (e.g. if we revise Lady Macbeth for two lessons and then - who knew! - the mock question is on Lady Macbeth) I can tell who has just parroted back my words and who has engaged with the character/theme fully.
• Deliberately avoiding a challenging text/question in the mock to enable all students to access it.

I can 100% guarantee no teacher is under predicting in order to keep any student at their school. We love it when they stay for 6th form and wish them well if they decide to spread their wings.

Is the school incentivised not to predict higher grades to avoid losing their best students to other 6th forms?

Is the predicted grade actually based on his mocks, or some computer generated figures based on SATS/entry tests in Year 7/a random number generator?

If you want the predicted grade for a sixth form application, you need to ask for one that is based on current attainment.
(Not even sure that sixth forms even check predicted grades tbh; so he could probably put anything down).

Your DS should be able to put down current assessed grade on his 6th form applications, too.

The predicted grade will have been generated by data from KS3. Your current results mean the teaching is going very well!

And do you know that that school offers places based on predicted grades? I would contact them and see if that is so. And are the PGs he has too low to be offered a place?

It could depend on a lot of things - off the top of my head:
Some teachers predict cautiously
The mock was easier than the final exam will be (omitted some tricky elements for example)
The teacher feels for whatever reason (perhaps based on class work too) that the lower predicted grade is more realistic
Students were suppported beforehand eg the Eng lit esssy was a question done in class a month before

I agree it’s unusual tho. What sort if disparity? And what subject?

I wouldn’t worry too much about sixth forms as IME (tho this doesn’t include very selective ones as none are round my way) they are interested above all in GCSE grades achieved.

All sixth forms are selective in the sense that places are conditional on GCSE results. It would be a good idea to apply for one option that would admit him if results are in line with the predictions.
Although it seems unusual to have mock results higher than predicted grades, it could be a sign that this will continue for the actual exams which is good. However it may also be that the school has taken into account that some of the areas that haven't been tested yet are harder when making the predictions.