Hi A.,
Our son, who is also 6 yrs old, behaved in the same manner. He has ALWAYS displayed symptoms of seperation anxiety. We thought as he got older it would improve. It didn't...until recently.
His pediatrician recommended us to a develop/behavioral pediatrician. After filling out numerous forms, having his teacher fill out a few forms, and meeting with the develop/behavioral pediatrician, our son was diagnosed with Generalized Anxiety Disorder (our son met with her also-without us). We discovered that his behavior, upon seperating from my husband and me (more so with me), was what helped him to focus throughout the day. By being able to attribute those 'I don't know or understand' feelings to SOMETHING, he was able to function.
He would have a tantrum at drop off, but would (more often than not) calm down within 20 mins, but on some days the crying would last all day.
After four years of trying different behavior/cognitive modification, and discussing the situation at great length with my husband, pediatrician (whom we trust completely!), and the develop/behavioral pediatrician (whom we also trust but don't know as well) we decided to try medication. (boy did I cry a lot of tears with that decision as it was SO against my husband and my philosophy!!!) He started taking the meds in December.
The difference in our son, since he started the medication, has been astronomical!
Although there is still repetitive questioning (you won't forget to pick me up Mommy? You won't be late, right Mommy? You'll be waiting in front of my classroom Mommy? You promise all these things, right Mommy? and you don't break promises. Right, Mommy?) the panic is gone from his voice, as well as the fear in his eyes! He also no longer runs after me, crying, when I turn around to leave the school.
I know with our son, when he is made a helper/assistant it helps him calm down because he feels he is in control of something; which is so opposite of how he normally feels. He constantly feels as if he has no control because his feelings of worry, fear, etc, have no foundation. He just knows he is feeling those bad feelings but doesn't know why; that is why the helper/assitant 'job' help him so much. The 'job' gives him something he can focus on and gives him control (not over the other kids mind you :-) just control in general).
I recommend keeping a tally of when her fits happen, how long they last, and what makes them stop. Also, speak to your pediatrician to see if he/she has any suggestions.
My biggest piece of advice...if you feel there is something going on, and are not content with the 'anwers', don't let people try and change you mind - listen to your instincts! We were told he would grow out of it (by our families. His pediatrician thought he would but wanted to wait and see); there was nothing wrong with him; and it is all normal little boy behavior because most boys are such 'Mama's boys'.
Don't let anyone try and 'convince' there is nothing wrong!!!
If my husband and I had listened, we would still be pushing our son off on some other adult so they could hold him back while I left the school grounds!
I hope this helps! Good luck!!!
J.