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CBA actually makes this pretty clear and says that just going abroad isn't going to make Tyler draft eligible in 2010.
To be eligible, a player like Tyler (who does not qualify as an "international player," even if he plays a year abroad -- more below) must meet 2 requirements:
1. He must be 19 years of age in the calendar year in which the draft is held; AND
2. at least 1 season must have elapsed since graduation of the class with which the player would have graduated had he graduated.
If you don't have both, you aren't eligible.
The exception to #2 is available to those who qualify as international players. But, "an 'international player' is a player: (i) who has maintained a permanent residence outside of the United States for at least the three (3) years prior to the Draft, while participating in the game of basketball as an amateur or as a professional outside of the United States; (ii) who has never previously enrolled in a college or university in the United States; and (iii) who did not complete high school in the United States."
It's not physically possible (to my knowledge) for Tyler to have maintained permanent residence outside of the United States for the three years prior to the draft if he departs the United States a year before the draft. Without doing that, he's not an "international player," and thus must meet the two requirements above. That means he has to wait until a full year after his high school class would have graduated to be draft eligible.