Would a teacher evaluation have more bearing if it’s from the head of department. Also, if your grades are mediocre doing the term but you got oustanding grades for GCSE and A Levels, would your grades matter?
I’m applying for US colleges btw.
- Not really. Keep in mind that teacher recommendations are not as relevant as your SAT/ACT scores, GPA, and essay so any"extra weight" ascribed to your recommender's status may not matter in the grand scheme of your application. Also unless your recommender notes it in the letter, you can't garuntee that the college will know that your recommender is a department head. Of course if the recommendation came from a well known professor, politician, or someone else of influence then that would actually carry some weight.
- My gut says that your grades would matter and your GCSE and A levels scores would be used like AP scores (for credit after admission and to add a bit of context to your grades). However my gut really isn't a reliable source. You might want to call the colleges or check their websites for information specific to international applicants.
Yeah she did mention it in the letter after signing her name. 
but thank you all the same
- Position of the person doesn't matter; quality of the recommendation does.
- No, grades matter the most. GCSE and A levels are nice to compare and see how you did overall, but grades are important.