According to publicly available information on the Cambridge Esol and ETS websites, Saudi’s seem to perform best in the speaking skill.
In both exams, listening comes second, though a little behind on average compared to speaking.
In IELTS, Saudi’s do worst in writing, but in the TOEFL iBT they do worst in reading.
So basically, reading and writing are the weakest skills.
What’s odd (in my opinion), is that I thought that as the TOEFL iBT is online, typing might be an issue. It seem’s not based on the statistics available.
Fundamentally, what the figures (for 2014) show, is that speaking is way ahead in terms of average performance, whereas listening, reading and writing are clustered closely together.
It’s difficult to read too much into these numbers, but one thing that policy makers should start focussing on, is the development of reading and writing abilities in the long-run, especially for those who are planning to travel overseas for further study or work.