Coached by Ron Estabrook at Chaparral High School in Scottsdale, Arizona, Sendlein was a four-year letter winner and three-year starter as a prepster.

He started varsity football early and became a first-team all-region choice at offensive tackle as a sophomore.

Sendlein also helped lead team to back-to-back Arizona 4A State Championships in 1999–2000 and a 28-game winning streak.

He racked up 157 tackles that year, his top game of his junior season was a 19-tackle performance against the Saguaro Sabrecats.

On his signing with the Cardinals, Sendlein said, "I had about 20 to 25 teams call to check on my status, but my agent and I felt like Arizona would be a good fit."