2009-10: Ladue skated in 27 games for Grand Forks Central HS in North Dakota as a junior. He scored 10 goals with 25 assists and had 18 penalty minutes. Central finished first in the East Region and were state champions; finishing with a 24-3 record. Ladue was selected by Lincoln in the 16th round (226th overall) of the 2010 USHL Entry Draft.
2010-11: Ladue joined the NAHL's Alexandria Blizzard, foregoing his senior season at Grand Forks Central to play junior hockey. He skated in 56 of 58 games for the Blizzard and scored 3 goals with 19 assists and 58 penalty minutes. Ladue's plus-18 plus/minus was second on the Blizzard behind Thomas Williams (+26). Alexandria finished first in the NAHL Central Division. Ladue played in three playoff games in the five-game series with Bismarck and was minus-two with 2 assists and 2 penalty minutes. Ladue was identified as a "Player to Watch" by Central Scouting but was not selected in the 2011 NHL Draft in his second year of eligibility.
2011-12: Ladue played for the USHL's Lincoln Stars and committed to playing college hockey at North Dakota in 2013-14. In 56 games for the Stars he led all Lincoln defensemen with 9 goals and had 25 assists; finishing plus-36 with 27 penalty minutes. Lincoln finished first in the West Division and reached the USHL playoff semifinals. In 8 playoff games Ladue was plus-two with 1 goal, 2 assists and 2 penalty minutes. Not among the 210 North American skaters in Central Scouting's final rankings prior to the 2012 NHL Draft, he was selected by Los Angeles in the sixth round (181st overall).