WA has special rules for teen drivers
WA State Licensing: Teens
During the first six months, no passengers except family, and then only one. No cell phone use with or without hands-free setup.
As a former (in one of my jobs) underwriter, the last thing you want is any teenager in a little convertible stickshift sports car. Over 80% of teens get into a wreck in the first six months of driving. A wreck is almost a certainty. So, think of your child's safety first. I suggest an old Volvo 240. Like a tank, underpowered, very safe.
Depending on who you are insured with, putting a teen in a miata might get your insurance non-renewed. And, even if accepted, astronomical rates.