Clark High School. (K.M. Cannon/Las Vegas Review-Journal) The historic halls of Clark High School in the central Las Vegas Valley aren’t as full as they were when junior Alex Martinez Vaca started attending classes there. Once-packed cafeteria seats now remain empty, he said as a handful of his remaining classmates trickled through Clark’s wide, pale yellow-tiled hallways. “At lunch, you can notice less crowds,” Martinez Vaca said. “It used to be really full and stuff, but not much anymore.” Like most schools in the Clark County School District, Clark High School’s student enrollment has declined over the last decade. Enrollment at Clark peaked at 3,411 students in the 2020-21 school year but has fallen to 2,721 this year — a nearly 700 student drop. Clark is expected to lose another 88 students over the next five years, district data shows.…