Charter schools have been a boon for Arizona education. The competition keeps traditional public schools sharp and gives parents and students choices.

The last thing the state's 535 charter schools need is a scandal that raises doubts about how well the money is spent. Lax purchasing rules are an invitation for abuse.

That's why a push for reform -- greater accountability and transparency -- should come from charter-school leaders. They have the most to lose if nothing changes.

The Arizona Republic's Anne Ryman found that about 40 non-profit charter schools paid $70 million to companies run by the schools' board members, executives or their relatives. No figures are available for for-profit charter schools, whose finances and activities are private.

The money paid for books, curricula, facilities repairs and administrative services. Some was forked over without bids, trusting board members to provide a good deal. When auditors noted a lack of documentation that schools were getting a good value, boards generally did nothing.

Arizona requires public and charter schools to seek oral or written bids for purchases over certain amounts. Charter schools, however, can seek an exemption as long as they promise all purchases will be in the best interest of the school, whatever that means. Nearly 90 percent of charters have been granted the exemption.

They have found creative ways to use it.

Three members of the Ernest Gaddie family make up the non-profit board of Happy Valley School in Peoria. The board contracts with Gaddie Curriculum & Education Consulting for a variety of services. Twice, auditors have questioned whether the school is getting a fair value. Twice, the board has said it would provide documentation, but the Gaddies declined Ryman's request to see it.

Since 2009, Great Hearts Academies has purchased nearly $1 million in books from a company owned by an officer of the non-profit. Six of the 15 Great Heart schools direct parents and students to that company, and no one else, for additional books.

The founders of Arizona's top charter, Basis, created a separate for-profit management company to provide everything from teachers to back-office functions. That puts salaries and most of the school's spending out of public sight. School founder Michael Block makes no apologies.

"Judge us by our results," he told Ryman.

Basis produces highly educated students, no question. The founders of other charter schools have noble motives. But that doesn't change a simple fact: They are using tax money. Although the whole idea of charter schools is to reduce red tape, that should never mean tossing out accountability.

Charter schools should be as transparent as public schools in how they spend our money. Checks and balances should guard against charters becoming cash cows for a well-connected few.

No-bid deals and a lack of transparency invite abuse. If rules do not change, a scandal will come. The backlash will hit all charter schools. It would be much better to change the rules now, and the charge should be led by charter schools and the state Board for Charter Schools. It is in their self-interest.