All people must have access to educational opportunities that meet their needs through Sustainable Development Goal 4. The goal requires education systems to obtain sufficient funds and use their resources properly. The relationship between public education spending and student academic performance remains disputed because countries achieve different results from their spending levels. This study uses country-level PISA 2022 scores, the first international assessment data published after COVID-19, to analyze public education expenditure as a share of GDP together with the pupil–teacher ratio and GDP per capita in relation to student academic performance across three subjects. Public education funding as a percentage of GDP is not statistically associated with PISA scores across 35 countries (r = −0.095, p = 0.586). The pupil–teacher ratio is a strong negative predictor of student performance (βˆ = −4.097, R2 = 0.312, p < 0.001). A three-variable regression model combining expenditure share, pupil–teacher ratio, and GDP per capita explains 59% of cross-country score variance (R2 = 0.592). High-income economies dominate the upper achievement tier, but several systems, notably Estonia and Poland, substantially outperform their GDP-predicted scores. The results indicate that education systems should focus resources on strengthening instructional capacity.