The Programme for International Student Assessment rated Scotland above the international average in reading and science, and average in maths.
The verdict, based on assessments of 15-year-olds in 65 countries, is the first on children educated wholly under a devolved curriculum.
Ms Smith said: "While Scotland compares well to other developed nations, there is still room for improvement.
"As Curriculum for Excellence was introduced this year, everyone is waiting to see how this affects Scotland's global standing. Literacy in Scotland leaves something to be desired. Trainee teachers must be properly equipped with essential skills in spelling and numeracy whilst at university or college."