In Flowers for Algernon by Daniel Keyes, when did Charlie's thinking—his thought process or strategy—change?

After the operation, Charlie expected immediate results, but because the changes were slow, he was unable to notice his developments. The first and major milestone for Charlie was beating Algernon. This also marked the onset of the remarkable changes that he was going through. Soon after, he was able to learn the spellings of different words, and Miss Kinnian introduced him to punctuation. He also found out that Frank and Joe were not his friends,...

After the operation, Charlie expected immediate results, but because the changes were slow, he was unable to notice his developments. The first and major milestone for Charlie was beating Algernon. This also marked the onset of the remarkable changes that he was going through. Soon after, he was able to learn the spellings of different words, and Miss Kinnian introduced him to punctuation. He also found out that Frank and Joe were not his friends, and they only made fun of him.

These changes continued at a rapid rate, and he understood his surroundings much better. He helped rearrange the machines at work and earned a bonus from Mr. Donnegan. In his 11th progress report, Miss Kinnian admitted to Charlie’s remarkable progress, but she was fearful of the uncertainties that lay ahead.

In summary, Charlie achieved noticeable changes on April 6th when he first beat Algernon. However, he personally recognized the changes when he first realized that Frank and Joe made fun of him all along. This made him view his past relationships differently, but also made him recognize his improved intelligence.