My son will be preparing for HSPT and was looking for Grammar and Vocabulary resources to improve his skills.
I always recommend William Strunk’s classic book, The Elements of Style. It is a great start.
Its 46 pages long, it costs $3 on Amazon,it can be read in a day, it will stay useful for a lifetime.
It is the most impactful book on writing I have ever read.
I like the videos on The Nature of Writing website. Also, the Purdue OWL.
Depends on how much time he has, and how high he is aiming, but I would recommend Meltzer’s “Ultimate Guide to SAT Grammar” and accompanying workbook as great resources.
No idea about vocabulary books, but my kid’s elementary school gave them access to a program, membean.com, that was very helpful and fun. Good luck to him!
I second the membean.com advice.
My son’s high school requires 15 minutes of membean, 3 times a week. They track it and he gets graded. It improved his vocabulary a great deal this past year.
Read The New York Times for 20 minutes every day. Best way to learn grammar and vocabulary is to experience it in use.