TILDEN — Every weekday morning, the rumble of buses dropping off students at McMullen County’s only public school gets drowned out by the heavy trucks whizzing by on Texas 16. Tilden is a small town, and with 235 students in pre-K through 12th grades, the school is small, too — even after enrollment jumped 42 percent in a year and a half. Outside, students can see the reason: drilling rigs in the distance. At recess,…