The third type of secular Bar Mitzvah was developed by secular Yiddishists in the United States before and after World War II. Rifkind's book includes a Hebrew translation of a Yiddish article from 1939 describing such an event. It sounds from the description that the family and friends were Labor Zionists. The party was in place of a synagogue service and the focus had shifted from God and the Mitzvot to Zionism, Yiddish and the Jewish people.
Source: wiktionary