He did not because people were starting to question his motive.
http://www.maxim.com/maxim-man/ahmed-mohamed-clock-truther-2015-9
turns out the clock he "made" was really just a clock from Radioshack that he took the casing off of and put into a briefcase. He set an alarm that he knew would go off during the middle of class. When he first showed it to a teacher, the teacher said neat, but be careful because it kinda looks like a bomb. He then takes it and sets an alarm to go off during the middle of class because he wanted to show his teacher what he had built, even though he did not build it.
It sure looks like the kid was trying to get a rise out of his teachers, and pretended to build something he did not. Turns out the school called his bluff and shit got real. He waited to let things clam down, but we once again will see reports coming out questioning what his purpose was.