Ndefo began his high school career at Elmont Memorial High School.[1] He helped lead team to a Class A state title as a sophomore.[2] Ndefo helped Elmont Memorial win the Nassau Championship as a junior. He finished with 22 points, 14 rebounds and five blocks in the title game and hit the game-winning buzzer-beating shot in the 58–56 win against South Side High School.[3] After his junior season, Ndefo transferred to Abraham Lincoln High School. He averaged 14 points and 9 rebounds per game as a senior. In January 2018, the New York Board of Education ruled Ndefo ineligible, causing him to miss the remainder of the season.[1] He committed to playing college basketball for Saint Peter's, the only Division 1 school to offer him a scholarship.[2]
As a freshman, Ndefo averaged 7.8 points and 5 rebounds per game.[4] Ndefo averaged 8.5 points, 5.3 rebounds, 2.4 blocks and 1.4 steals per game as a sophomore.[5] He was named MAAC Defensive Player of the Year, MAAC Sixth Man of the Year, and Third Team All-MAAC.[6][7] Ndefo posted a career-high seven blocks against Siena on January 23, 2021.[8] On February 26, he scored a career-high 22 points in a 66–52 win against Rider.[9] As a junior, Ndefo averaged 13.7 points, 6.5 rebounds, 1.5 assists and 1.4 steals per game while shooting 50 percent from the floor.[10] His 3.6 blocks per game led Division 1 in that category, and he was the shortest player to lead the nation in blocked shots per game since William Mosley of Northwestern State in 2011.[11] He was named to the First Team All-Maac as well as repeating as MAAC Defensive Player of the Year.[12] Following the season, Ndefo entered the transfer portal, but ultimately returned to Saint Peter's.[13] On February 4, 2022, he scored 14 points and had a program-high 11 blocks in an 83–74 victory over Quinnipiac. Ndefo also surpassed the 1,000 point mark during the game.[14] He was named to the Third Team All-MAAC as well as MAAC Defensive Player of the Year for the third season.[15][16]