The 48-year-old Justice League star put on his best suit to join Garner for a monumental moment in their youngest daughter's life.
The former married couple was photographed together in Los Angeles on Monday, just one day after Affleck joined J Lo and her teenage twins for a family dinner.
Affleck dressed in dark-colored slacks and a matching suit jacket with a light green tie to celebrate 12-year-old Seraphina's sixth-grade graduation.
Garner looked lovely for the festivities, wearing a white-and-black floral-patterned dress.
The graduate stood between her parents and looked like the life of the party in a long, black dress.
The exes put on happy faces for their day of co-parenting.
Following the ceremony, Affleck jumped into the car with Garner and their three children -- Violet, 15, Seraphina, and Samuel, 9 -- and went to lunch as a family.
Ironically, just hours earlier he was having dinner with J Lo and the Love Don't Cost a Thing singer's 13-year-old twins, Emme and Max.
Despite being caught heavily making out with J Lo at the dinner table, her kids are cool with their mom's relationship with Affleck.
The duo and her children were spotted at Nobu in Malibu on Sunday.
"Ben and her kids seemed comfortable together," a source told PEOPLE about the dinner. "The kids kept chatting with Ben. Ben seemed great. He was smiling and laughing. They ordered a lot of food to share. Ben had a Diet Coke."
"Jen and Ben sat next to each other and were very affectionate," the insider revealed. "They held hands under the table."
While Affleck has now met J Lo's two kids -- who she shares with ex-husband Marc Anthony -- the couple has yet to introduce Max and Emme to the Academy Award winner's three children.
Radar is told the new couple plan on connecting their children soon.
“Jen and Ben rushed into getting back together. They didn’t mess about jumping back into the relationship; however, they are taking things much slower when it comes to introducing their children,” sources tell Radar.
“Jen’s kids got very close with Alex Rodriguez’s family which is why they are not rushing. Both sets of children know who their parent is dating and at some point, both families will meet, just not yet," they added.
J Lo and Affleck have been inseparable since she ended her engagement to Alex Rodriguez in April.