original: He excelled in history throughout his school years while his grades in other subjects remained average.
simplifications: He excelled in history during his school years while his grades in other subjects remained average. He had high grades in history while in school but average grades in all other subjects. In school he was good in history, but his other grades were average. He excelled in history, while having average grades in other subjects. He performed well in history during his school years, but his grades in other subjects were average. He was good in history throughout school. His grades in other subjects were average. He did well in history at school. He was average at other subjects. He did great in history during his school years but his grades in other subjects stayed average. He shined in history during his school years, but grades in other subjects were average. He excelled in history throughout his school years, while his graduation in other subjects remained average.