The Language Arts and Writing (LAW) component of EPGY for the elementary grades covers grammar, and my kids use it. EPGY also has grammar courses for junior high school students, descriptions copied below. Has anyone tried them?

http://epgy.stanford.edu/courses/english/secd.html
EG20 Grammar and Style of the Sentence

This is a self-paced grammar course designed to help 7th to 12th grade students understand grammar and make stylistic choices informed by their knowledge of grammar. Topics include effective subject and verb choice, active and passive voice, clause coordination and subordination, sentence fragments, comma splices and run-together sentences, and phrasal modifiers (including verbal constructions or finite verbs). The course runs over the web. We strongly recommend that students enrolled in the W10 or W11 series also take EG20 concurrently.

Completion time: 1 quarter.

Please note: The EG20 course requires the Windows operating system and will not function with the Mac OS.

EG21 Grammar and Style of the Sentence II

The second of two self-paced grammar courses, EG21 is designed to help 7th to 12th grade students both further their understanding of grammar and make informed stylistic choices in their own writing. Topics include: verb moods, tense and irregularities; pronoun case, antecedents, appositives and usage; dangling modifiers, and selected punctuation topics. The course runs over the web. We strongly recommend that students complete EG20 before enrolling in EG21.

Completion time: 1 quarter.