@ucbalumnus Davis, like most other UCs, runs two 6 week summer sessions. The other options you are seeing are for very specific, unique programs.
@3boysmom3, Davis is very quiet over the summer. To my knowledge, they don’t have a Freshman Summer Start Program similar to what is offered at UCSB. The only program I am aware of is for international students. At UCSB, he would be able to live in the dorms. At Davis, he would need to sublet an apartment. Taking a summer course would help orient him on campus. It will also give him a few more units which will help give him better registration times in the future. I don’t know that it will provide groups or connections better than the freshman dorm experience.