The event has been strictly-orchestrated by the military regime that seized power in 2014.
The government is offering the day-long course free of charge.
King Vajiralongkorn is holding huge celebrations, turning his birthday into a public holiday and releasing 1,066 symbolic sea turtles.
Some of those found guilty were also convicted of rape, organized transnational crime and forcible detention leading to death.
Monday marks the third anniversary of a military coup that has seen a crackdown on dissent in the Asian country.
The U.K.'s ambassador to Thailand will speak Wednesday at the International Day Against Homophobia, Transphobia and Biphobia in Bangkok.
The royal ceremony is an ancient Brahminical rite that heralds the start of the new rice-growing season.
Barisan Revolusi Nasional (BRN) is thought by observers to be the main faction responsible for the decades-old insurgency in the Muslim-majority southern provinces of Yala, Pattani and Narathiwat.
Protests in Venezuela, the conscription of transgender women in Thailand and more in The Week in Pictures.
Jatupat Boonpattararaksa is accused of lese-majeste, or insulting the monarchy.
Prime minister stresses that the government is working as normal with a regent in place until the crown prince assumes the throne.
Crown Prince Maha Vajiralongkorn wants to mourn with the people before assuming the monarchy after King Bhumibol Adulyadej's death.
King Bhumibol's long-anticipated passing has raised questions about the suitability of his heir.
Thais have gathered outside the hospital where he passed away to pay their respects.