[1] He attended Cy-Fair High School, playing as a cornerback, wide receiver and return specialist and helping them win the Class 6A championship with a 15–0 record during his senior year.
[2][3] He posted 38 tackles and six interceptions during his senior season, earning first-team all-district honors.
[2] In 2020, he played ten games, starting the final four, and tallied 30 tackles, two of which were for a loss, four pass breakups and two interceptions.
[4][5] Hallett was named honorable mention all-conference in 2021 after starting all 14 games and making 70 tackles, 2.5 TFLs, nine pass breakups, three interceptions and two forced fumbles.
[4] In his final year, he started all 13 games and earned second-team all-conference honors while posting 54 tackles, four TFLs and nine pass breakups with two forced fumbles, additionally being a semifinalist for the Jim Thorpe Award, given to the best defensive back nationally.