1. **State the problem:** We know that 20% of the students brought their lunch, which corresponds to 34 students. We need to find the total number of students in the school, which corresponds to 100%. 2. **Set up the proportion:** Let $x$ be the total number of students. Since 20% corresponds to 34 students, we write the proportion: $$\frac{20}{100} = \frac{34}{x}$$ 3. **Solve for $x$ by cross-multiplying:** $$20 \times x = 100 \times 34$$ $$20x = 3400$$ 4. **Divide both sides by 20 to isolate $x$:** $$\cancel{20}x = \frac{3400}{\cancel{20}}$$ $$x = 170$$ 5. **Interpretation:** There are 170 students in total at Ridgewood Junior High School. **Final answer:** $$\boxed{170}$$