ANSWER:

Nationally, the average ratio of students to school psychologists is approximately 1,350 to 1,400 students to each full-time psychologist.  However, the National Association of School Psychologists (NASP) recommends that the ratio of school psychologists to students should not exceed 1,000 students to 1 school psychologist.  Also, NASP recommends that school systems that deploy psychologists to provide comprehensive and preventive services (e.g., behavioral interventions, consultations, evaluations, and crisis response) should use a ratio that does not exceed 500 to 700 students to 1 school psychologist.  NASP recommends that when school psychologists are assigned to work primarily with students with intensive needs (e.g., students with autism spectrum disorders and students with significant emotional or behavioral disorders), the student to school psychologist ratio should be even lower. 
The FY 2014 budget includes 95.0 FTE psychologist positions.  Of these, 68.5 FTE psychologist positions are budgeted in the Department of Student Services (DSS).  These staff provide services to all students in the 196 comprehensive elementary, middle, and high schools, including those with more intense needs, such as students with autism spectrum disorder and those enrolled in Fundamental Life Skills and School/Community-Based programs.   
There are 18.5 FTE school psychologist positions budgeted in the Department of Special Education Services as follows: 

Also, there are 5.0 FTE psychologist positions in the budget for the Bilingual Assessment Team and 3.0 positions are budgeted in the Prekindergarten and Head Start budget.

The most recent report of the Maryland State Department of Education (MSDE) regarding school psychologists employed in Maryland used data collected during the 2011–2012 school year.  As indicated below, data showed that the ratio of total student enrollment per psychologist in larger Maryland school systems ranged from 658 students per psychologist (Baltimore City Public School System) to 1,522 students per psychologist (Montgomery County Public Schools).

The following information shows how Maryland school systems, including MCPS, employ a range of practices and formulas for allocating psychologists. 
Anne Arundel County Public Schools (AACPS) 
AACPS maintains a ratio of approximately 1,200 students to 1 psychologist.  AACPS allocates school psychologists to schools as follows:

AACPS allocates an additional 0.2 FTE psychologist for regional special education programs, such as Multiple Intensive Needs Classes, and regional programs for students with Autism Spectrum Disorders and students with Emotional Disabilities (ED).
Baltimore City Public School System (BCPSS) 
BCPSS allocates a full-time school psychologist for every 850 students. 

Baltimore County Public Schools (BCPS) 
BCPS currently staffs school psychologists at a ratio of approximately 1,250 students for
1 psychologist.  Since 2005, BCPS has included a 0.6 FTE school psychologist allocation in its operating budget whenever a new school opens.  BCPS does not allocate school psychologists to schools by a specific formula. 
Frederick County Public Schools (FCPS)
FCPS does not have a formula for allocating psychologists. 
Howard County Public Schools (HCPS) 
HCPS maintains a ratio of approximately 800 students to 1 psychologist.  HCPS applies the following formula to allocate FTE psychologists to schools and special education programs:

Prince George’s County Public Schools (PGCPS) 
PGCPS does not have a staffing formula for psychologists.

Montgomery County Public Schools (MCPS)
MCPS does not have a staffing formula for psychologists, although prior to the beginning of the fiscal crisis in FY 2009, positions were added for new schools.  In fact, in FY 2008 there were 102.8 psychologist positions budgeted. Since FY 2009, MCPS has had to cut hundreds of positions and there has been little opportunity to add positions without cutting others. In 2012, the Joint Collaboration Committee for Psychological Services (JCCPS) developed a staffing and hiring proposal based upon school levels (i.e., elementary, middle, or high), number of students, and special programs (e.g., Extensions, Stephen Knolls, Transition Training for Independence, etc.).  At that time, the JCCPS staffing and hiring proposal recommended a ratio of 1,500 students to 1 psychologist.

Using FY 2014 projected enrollment (excluding charter school and Gateway to College enrollment) and a ratio of 1,500:1, an additional 5.75 FTE psychologist positions would need to be added to the budge at a cost of $804,660, including employee benefits.  The cost of a 1.0 FTE psychologist position is $139,941, including benefits.