Third grade (also 3rd Grade or Grade 3) is the third year of formal or compulsory education. It is the third year of primary school. Children in third grade are usually 8–9 years old.

In Australia, this level of class is called Year 3. Children generally start this level between the ages of eight and nine.

In Brazil, third grade is the terceiro ano do Ensino Fundamental I, in this case, children begin their first year of elementary school at age 6 or 7 depending on their birthdate. Therefore, the 3rd year of elementary school is typically for students of 8 (96 months)–9 years (108 months) of age. All children students must be 8 years old before the cut-off date.

In England, the year of school that is the same age as 3rd Grade is Year 4, which is the fourth year of compulsory education. Most children start one year earlier however, in the Reception class. Welsh pupils are in their fourth full year of compulsory education. In Northern Ireland and Scottish pupils are in "Primary 4", their fourth year of compulsory education.

In Canada, the year is called Grade 3, and the pupils are known as "3rd grade".

In France, children aged 8 join CE2 ("Cours élémentaire deuxième année"), the third school year of primary school. It was formerly called "neuvième" (ninth year before Terminale, the "baccalauréat" year).

In Germany, the equivalent grade is 3.

In Greece, the third school year of primary school is referred to as Third Grade of Primary (Triti - Τρίτη Δημοτικού)..