To check balance explicitly:
tabulate country_id if education_spend == constant_in_time stata panel data
F(3,597) = 34.21, Prob > F = 0.000 Within R-squared = 0.28, Between R-squared = 0.41, Overall = 0.35 rho = 0.67 (fraction of variance due to country effects) 597) = 34.21