I'm a high school Mathematics teacher and I want to issue some research articles for highschool students to improve their math problem resolve skills. Is there any valuable Math journal for high school students (grades 12, 11) that can issue Mathematics articles and be citeable by Google Scholar?
The College Mathematics Journal is the closest I know to what you are looking for, because it is geared toward "the first two years", which nowadays would correspond to high school level in the better schools.
Other than that, there is the Montana Mathematics Enthusiast that publishes popular articles ("Montana" was eventually removed from the title).
Journal of Humanistic Mathematics is an unusual one that may have some accessible stuff now and then.