Tutu sits quietly on a chair in a classroom while his mother conducts a chemistry lecture on May 7, 2015. [Photo/CFP]

Zhang returned to her job back in February after taking a semester off to attend Tutu while he was in hospital. Due to Tutu's worsening health, Zhang brings him to classes while she teaches--both as a comfort to her ailing three-year-old son and as a way to watch him while she earns what money she can from her job.

The mother donated her bone marrow to help her son, and several of her students have created an online campaign to help raise funds for Tutu's surgery. Zhang has managed to gather 300,000 yuan for Tutu's bone-marrow transplant, but it's less than half of what she needs to meet the 700,000-yuan surgery costs.