With the exception of threatening the teacher (if that's even true), kid and parent has a case.
The history of legal challenges to the Pledge of Allegiance - National Constitution Center
The Supreme Court then took the unusual step of ruling against the Jehovah's Witnesses in a legal fight against the Pledge and reversing its own ruling within three years.
First in 1940 in the case of
Minersville v. Gobitis, the Court said that a public school could force students who were Jehovah's Witnesses to salute the flag and say the pledge. Justice Felix Frankfurter said in the majority opinion that “conscientious scruples have not, in the course of the long struggle for religious toleration, relieved the individual from obedience to a general law not aimed at the promotion or restriction of religious beliefs.”
However, in 1943, the Court changed its course in
West Virginia State Board of Education v. Barnette, where the majority said that
“the Free Speech clause of the First Amendment prohibits public schools from forcing students to salute the American flag and say the Pledge of Allegiance.”
“If there is any fixed star in our constitutional constellation, it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion, or other matters of opinion or force citizens to confess by word or act their faith therein. If there are any circumstances which permit an exception, they do not now occur to us,” said Justice Robert Jackson in his opinion