Wáng lǎoshī shēngbìng le, jīntiān Lǐ lǎoshī lái dàikè.
Teacher Wang is sick, so Teacher Li is substitute-teaching today.
Tips
usage
代课老师 is a common compound meaning 'substitute teacher'. In rural China, 代课老师 often refers to unqualified locals who fill in where there aren't enough certified teachers.