Error in MySQL via PHP

Why doesn’t it work? How to put a variable

      $result = mysql_query("SELECT `school` . `school`,  `street`
       FROM
      `datacenter`, `school` 
        WHERE
     `datacenter` . `id_school` = `school` . `id_school` 
      AND
   `datacenter` . `name` = '.$name_teacher.'");

Answer 1, authority 100%

    $result = mysql_query('SELECT `school` . `school`,  `street`
FROM
`datacenter`, `school` 
WHERE
`datacenter` . `id_school` = `school` . `id_school` 
AND
`datacenter` . `name` = "'.$name_teacher.'"');