This is the 677th most frequent Latvian word.
piedalījās
"Participated."
In this sentence, 'piedalījās' means that he actively took part or was involved in the activity of the school concert.
Viņš piedalījās skolas koncertā.
He participated in the school concert.
Here, 'piedaloties' is the present active participle of 'piedalījās', implying active participation at the time of achieving the record.
Piedaloties maratonā, viņa sasniedza jaunu personīgo rekordu.
By participating in the marathon, she achieved a new personal record.
'Piedalījāmies' is the first person plural past form of 'piedalījās', indicating our involvement in the event in the past.