From those who have taken it, had you completed a single HS course (Honors?) or also AP Chem?
It’s been stated here several times that only one year is required. CB’s Subject Test Student Guide says “One-year introductory chemistry course at the college-preparatory level”
But my older D said one of her friends (top 5% in her class) took it after AP and still found it difficult. Our school’s gifted program lead also used to teach AP Chem and said many of his students took it after AP.
It really depends on how in depth honors first year at your kid’s high school is. Ours is very good and one of my kids took it in June of sophomore year and scored mid 700s. She was not taking AP until senior year.
Does your kid’s first year chem class let them use extensive lists of ions, formulas, etc on exams, or do they have to memorize them?
There is no formula reference sheet on the subject test, there is on the AP.
My other kid took it after the AP test junior year. They were a grand total of 10 points apart.
Thanks for the feedback. They had a quiz early in the second 9 week period on polyatomic ions - had to write formulas from names and vice-versa - for 30’ish of them - and recently a major test on formula names that was similar.
She took the “What’s on the test” list to her teacher to see what she will need to study independently. From your two test scores, it sounds perfectly reasonable to do it after a single course, with appropriate prep. It would be nice to get Subject Tests out of the way.
(btw, curious…FT Vicki?)
Yes that is me. 
Take a practice test in May, study up on any areas lacking and June test should be fine.
It varies so much by high school. There are area high schools I tutor kids from that in no way prepare kids for the subject test after first year.
Thank you. Very helpful